Abstract: Airborne target detection in the infrared has been classically known as infrared search and track or IRST. Here, the target is “unresolved”. The detection range is an important and systematic indicator of the IRST system, which directly affects the system's ability to perform tasks and its effectiveness. It is an important basis for evaluating the system's performance. For high-altitude IRST system, the detection range is closely related to every link in the entire imaging process, such as the target, background, atmosphere, optical system, and imaging detector, etc. This paper will start from the infrared radiation characteristics of the aircraft target and combine the atmospheric transmission to give the radiation intensity difference between the target and the background in the mid wave and long wave bands. Based on the point source target/background signal-to-noise ratio model, the performance comparison analysis of the mid wave and long wave performance are carried out, which has reference significance for the design and analysis of IRST systems.